Unstructured Caster optimization

I'm guessing you mean:

Charmed Life, Major Heroic Virtue (HoH:TL, page 104)

"Fortune smiles upon you, often protecting you from the random consequences of adventure. You have the Luck virtue, and whenever you roll a 0 on a stress die in dangerous or deadly circumstances, you may spend a Confidence point to reroll it rather than checking for a botch. This should be applied in chaotic circumstances, not calculated efforts, since luck must play a factor to make use of this virtue — for example, charging into a rain of arrows or diving off a sheer cliff are appropriate actions, but not forging a letter or following a set of tracks."

Believe it or not, I know the answer because I was just yesterday browsing the old PdP campaign Unknown Cargo (En Route to Visby, near the bottom of page 1) - where Ovarwa's character used it!